An infrared sensor or other infrared imaging device generally must be cryogenically cooled for optimal performance. Accordingly, the infrared sensor generally is sealed in a vacuum-insulated container called a dewar, which is coupled to a compressor for circulating a cooling fluid through the dewar to maintain a temperature below ambient temperature.
When a sensor is used on a moving platform, such as a vehicle like a ship or an airplane, motion of the platform and motion of the sensor make optimal performance of the sensor more difficult. The relative motion of the sensor to a scene detectable by the sensor creates several problems. To ensure that the scene visible to the sensor is oriented to correspond to a desired coordinate system, rotation of the sensor platform must be compensated for. This is called rotation registration. In addition to maintaining a desired orientation of the scene for the sensor, the scene must be held in a relatively fixed position relative to the sensor's field of view. If the scene is moving relative to the sensor, for example, apparent rotation due to platform rotation, the scene may be blurred or not captured at all.
To date the primary method used to compensate for relative motion between the sensor and the scene is to use a motorized prism through which the scene is viewed. Another method of motion compensation uses algorithms to electronically stabilize the scene. Although faster electronics and better sensors continue to improve this method, it still often depends on the scene moving slowly enough for the sensor to capture an image and for the algorithm to compensate for the motion electronically.